Method for synchronizing the bi-directional transmission of data

ABSTRACT

The invention relates to a method for synchronizing a bi-directional transmission of data between a transmitter and a receiver based on the transmission of frames ( 10 ) having a predefined bit length, with a predefined first bit length ( 20 ) being provided in each frame ( 10 ) for the transmission of data from the transmitter to the receiver and a predefined second bit length ( 30 ) for the transmission of data from the receiver to the transmitter, with a trigger pulse ( 40 ) being sent to the receiver parallel to and independently from the transmission of the data between the transmitter and receiver, which pulse triggers a data collection process at the receiver, wherein the frame ( 10 ) has a time slot ( 50 ), during which no information is transmitted from the transmitter to the receiver and also not from the receiver to the transmitter, and wherein the trigger pulse ( 40 ) is transmitted from the transmitter to the receiver during this time slot ( 50 ).

The present subject matter relates to a method for synchronizing thebi-directional transmission of data in accordance with the exemplaryembodiments disclosed below.

Methods are known for the bi-directional transmission of data, accordingto which data is transmitted between a transmitter and a receiver. Thesemethods are based on the transmission of frames having a predefined bitlength, wherein in each frame a predefined first bit length is providedfor transmitting data from the transmitter to the receiver and apredefined second bit length for transmitting data from the receiver tothe transmitter. For example, in the first bit length a transmitter mayrequest data from the receiver, which data the receiver then transmitsto the transmitter in the second bit length. Parallel to this process,independently from the method for the bi-directional transmission ofdata, a trigger pulse is transmitted from the transmitter to thereceiver, which is used to trigger a collection of data at thereceiver's end, for example the collection of the data subsequently tobe transmitted to the transmitter. The trigger pulse is completelyindependent from the data transmission between the transmitter and thereceiver and in particular it is not precisely adjusted to the framelength with respect to its pulse length. According to the familiarmethods, the trigger pulse is digitized and then transmitted, wherein asa result of the digitization temporal inaccuracies may occur in thelength of a bit, for example approximately 1 μs. Such temporalinaccuracies, however, are unacceptable for many applications, forexample for high-resolution position measurements using an encoder.

It is therefore the object of the invention to provide a method, whichenables highly precise synchronization between the trigger pulse and thedata transmission between the transmitter and the receiver.

The object of the present subject matter is achieved by a method withthe characteristics according to the exemplary embodiments disclosedbelow.

Advantageous embodiments and further developments of the invention aredisclosed in the dependent claims.

The method according to the invention for synchronizing thebi-directional transmission of data between a transmitter and areceiver, based on the transmission of frames having a predefined bitlength, is characterized in that the frame has a time slot, during whichdata is neither transmitted from the transmitter to the receiver norfrom the receiver to the transmitter, and that the trigger pulse duringthis time slot is transmitted from the transmitter to the receiver.Consequently, the digitization of the trigger pulse can be eliminatedbecause the trigger pulse can be transmitted to the receiver directlywithin the time slot. As a result, temporal inaccuracy caused by thedigitization process is avoided, and precise synchronization between thetrigger pulse and the data collection by the receiver is guaranteed,since the data collection is performed without time delay precisely atthe time at which the edge of the trigger pulse reaches the receiver,which delay would be caused by the digitization of the trigger pulse andthe transmission of the trigger pulse, which occurs independently of thedata transmission.

It is preferable if the length of the time slot ranges between 3 and 8bits. This provides a sufficiently long time window, during which thetrigger pulse, particularly the edge of the trigger pulse triggering thedata collection at the receiver, can be transmitted.

Advantageously, the first bit length and the second bit length areprovided in the frame separated by several time delay bits, preferably 4to 7 time delay bits. In this way, it is prevented that the receiverwill already attempt to transmit data to the transmitter while data isstill being transmitted from the transmitter to the receiver.

According to an advantageous embodiment of the invention, the time slotwithin the frame is provided within the first bit length. Thisguarantees that no data is transmitted from the receiver to thetransmitter, so that no additional time delay bits are required.

In general, the trigger pulse spacing is not precisely adjusted to aframe length. While in this case, during a first transmission of thetrigger pulse, a transmission would occur within the provided time slotwithin the frame, the trigger pulse would shift within the time slotwhen several transmissions are to take place. To guarantee that thetrigger pulse is also transmitted always within the provided time slot,even in the event of discrepancies between the trigger pulse spacing andthe frame length, according to a particularly preferred embodiment ofthe invention one or more stuff bits are inserted, preferably directlybefore the first bit length, as a function of the trigger pulse spacing.The number of stuff bits to be inserted is defined by the shift of thetrigger pulse position within the time slot between the precedingconsecutive frames.

Advantageously, the stuff bits are inserted evenly distributed acrossseveral frames, particularly when a large number of stuff bits arerequired, so that substantially even data transmission can beguaranteed, despite the insertion of additional bits.

It is preferable if the number of stuff bits is greater than or equal toN, with N stuff bits replacing one synchronization frame, respectively.Such synchronization frames comprise additional information with respectto the synchronization between the transmitter and receiver, for examplea predefined bit sequence, which the receiver recognizes and is able touse for further synchronization.

It is preferable if N is equal to 5 or 6, since a bit sequence of fiveor six bits is sufficient to exchange additional information withrespect to the synchronization between the transmitter and receiver.

Typically, the length of the first bit length is at least 14 bits, thelength of the second bit 30 bits. The length of a frame is at least 60bits and no more than 120 bits, depending on the number of stuff bitsthat have been inserted.

The data is preferably exchanged between a controller of the transmitterand measuring units of the receiver, wherein the measuring units in aparticularly preferred embodiment are configured as position measuringunits, since particularly for the determination of positions, forexample with rotary encoders, high accuracy and exact synchronization isrequired between the trigger pulse and the data transmission between thetransmitter and the receiver.

The system according to the present subject matter comprises atransmitter and a receiver, between which data is transmittedbi-directionally, wherein the transmission of the data is carried outwith the method according to one or more of the disclosed exemplaryembodiments. In certain exemplary embodiments, it is preferable if thedata is exchanged between a controller of the transmitter and measuringunits of the receiver, wherein particularly the measuring units areconfigured as position measuring units, preferably as rotary encoders.

The invention will be explained hereinafter by way of example withreference the description of the FIGURES, wherein:

FIG. 1 is a schematic illustration of a frame according to theinvention.

FIG. 1 shows a frame 10 having a regular and therefore minimum bitlength of 60 bits. Within the frame 10, at the beginning of the frame afirst bit length 20 is provided, which typically has a length of atleast 14 bits and is intended to transmit data from a transmitter to areceiver. This may be, for example, a request for data.

Within the frame 10, data is transmitted bi-directionally. The first bitlength 20 is followed by a second bit length 30, which typically has alength of 30 bits and is intended to transmit data from the receiver tothe transmitter. In this second bit length, for example, the datarequested by the transmitter is transmitted from the receiver to thetransmitter. The second bit length 30 is shown graphically verticallyoffset from the first bit length 20 to illustrate that in this case thedata is transmitted in the opposite direction via the data line.

Advantageously, the first bit length 20 and the second bit length 30 areseparated by several time delay bits 60, preferably by four to no morethan seven time delay bits 60, which ensure that the transmission ofdata from the receiver to the transmitter and the transmission of datafrom the transmitter to the receiver do not overlap. Seven time delaybits 60 correspond to a time delay of 1.12 μs.

The second bit length 30 is again followed by several time delay bits65, preferably four to no more than seven time delay bits 65, in orderto exclude the data transmissions from intersecting.

Within the first bit length 20 a time slot 50 is provided, within whichno data is transmitted from the transmitter to the receiver, and alsonot vice versa, however within which the trigger pulse, particularly theedge of the trigger pulse, is transmitted directly from the controllerof the transmitter to the receiver. Consequently, a digitization of thetrigger pulse can be eliminated, which could result in a time delay. Inthis way, exact synchronization is guaranteed between the trigger pulseand the data collection by the receiver triggered by the trigger pulse.The length of the time slot 50 is approximately 3 to 8 bits in order toguarantee transmission of the trigger pulse 40 still within the timeslot 50, even in the event of possible shifts of the trigger pulse 40within the time slot 50. The length of the first bit length 20 thereforeincreases from regularly 14 bits by the corresponding number of bits forthe time slot 50, for which reason the length of the first bit length 20is listed as “at least 14 bits”.

When the distance of the trigger pulses 40 and the length of the frame10 have been precisely adjusted to each other, the edge of the triggerpulse 40 within each frame 10 is transmitted relative to the frame 10 onthe same position within the time slot 50. However, since the triggerpulse 40 is generated independently from the data transmission betweenthe transmitter and the receiver, this is generally not the case. Whileduring a first transmission of the trigger pulse 40 a transmission wouldbe carried out within the provided time slot 50 inside the frame 10,following the transmission of several frames 10, however, the triggerpulse 40 would shift within the time slot 50, specifically compared tothe transmission in the previous frame 10 it would take place soonerwhen the distance of the trigger pulses 40 is shorter than the length ofthe frame 10 and it would be later than the transmission in the previousframe 10 when the distance of the trigger pulses 40 is greater than thelength of the frame 10. A comparison of the positions of the triggerpulses 40 in two consecutive frames 10 can therefore allow a conclusionof the differences between the distance of the trigger pulses 40 and thelength of the frames 10. To guarantee that the trigger pulse 40 isalways transmitted within the provided time slot 50, even in the eventof variances between the distance of the trigger pulses 40 and thelength of the frames 10, one or more stuff bits 70 are inserted directlybefore the first bit length 20 as a function of the distance of thetrigger pulses 40. The number of stuff bits 70 to be inserted is herebydefined by the shift of the position of the trigger pulse 40 within thetime slot 50 between the preceding consecutive frames 10, since theposition of the edge of the trigger pulse 40 relative to the frame 10within the time slot 40 is known from the preceding frames 10 and at thesame time the amount by which the position of the edge of the triggerpulse 40 has shifted is also captured. At a maximum, however, the numberof stuff bits 70 to be inserted is equivalent to the number of bits thatthe frame 10 contains, in the present case 60. Such a high number ofstuff bits 70 is required when the position of the edge of the triggerpulse 40 within the time slot 50 is slightly sooner than expectedcompared to the previous frame 10. When, for example, this many stuffbits 70 must be inserted, they are preferably evenly distributed acrossseveral frames 10. When, for example, fifty stuff bits 70 must beinserted, these are preferably not inserted before the subsequent firstbit length 20 as one block of fifty stuff bits 70, but for example intofive consecutive frames 10 in blocks of ten stuff bits 70 each or intoten consecutive frames 10 in blocks of five stuff bits 70 each, in orderto guarantee substantially even data transmission, even when inserting alarge number of stuff bits 70.

So as to use the stuff bits 70 also for the transmission of usageinformation, N stuff bits 70 are replaced with a synchronization frameas soon as the number of stuff bits 70 is greater than or equal to N.Such synchronization frames comprise additional information with respectto the synchronization between the transmitter and receiver, for examplea predefined bit sequence, which the receiver recognizes and is able touse for further synchronization. This predefined bit sequence shouldhave the maximum possible number of bit value changes and no constantcomponent in order to guarantee the most reliable transmission anddetection of the bit sequence by the receiver as well as the mostprecise synchronization possible. It is preferable if N is equal to 5 or6, since a bit sequence of five or six bits is sufficient to exchangeadditional information with respect to the synchronization between thetransmitter and receiver.

The method is preferably used for the transmission of data between acontroller of the transmitter and measuring units of the receiver. Inparticular, the measuring units are configured as position measuringunits. Particularly for position measuring units, such as rotaryencoders, the time requirements are especially high in order toguarantee exact position determination, so that in this case the exactsynchronization between the trigger pulse and data transmission betweenthe transmitter and receiver is particularly advantageous.

1. A method for synchronizing a bi-directional transmission of databetween a transmitter and a receiver based on the transmission of frameshaving a predefined bit length, with a predefined first bit length beingprovided in each frame for the transmission of data from the transmitterto the receiver and a predefined second bit length for the transmissionof data from the receiver to the transmitter, with a trigger pulse beingsent from the transmitter to the receiver parallel to and independentlyfrom the transmission of the data between the transmitter and receiver,which pulse triggers a data collection process at the receiver,characterized in that the frame has a time slot, during which noinformation is transmitted from the transmitter to the receiver and alsonot from the receiver to the transmitter, and that the trigger pulse istransmitted from the transmitter to the receiver in non-digitized formduring this time slot.
 2. The method according to claim 1, characterizedin that the length of the time slot is 3 to 8 bits.
 3. The methodaccording to claim 1, characterized in that the first bit length and thesecond bit length are provided in the frame separated by some time delaybits.
 4. The method according to claim 1, characterized in that the timeslot within the frame is provided within the first bit length.
 5. Themethod according to claim 1, characterized in that one or more stuffbits are inserted depending on the trigger pulse length.
 6. The methodaccording to claim 5, characterized in that the stuff bits are insertedevenly distributed across several frames.
 7. The method according toclaim 5, characterized in that N stuff bits are replaced with onesynchronization frame when the number of the stuff bits is greater thanor equal to N.
 8. The method according to claim 7, characterized in thatN is equal to 5 or
 6. 9. The method according to claim 1, characterizedin that the length of the first bit length is at least 14 bits.
 10. Themethod according to claim 1, characterized in that the length of thesecond bit length is at least 30 bits.
 11. The method according to claim1, characterized in that the length of a frame is at least 60 bits andno more than 120 bits.
 12. The method according to claim 1,characterized in that the data are exchanged between a controller of thetransmitter and measuring units of the receiver.
 13. The methodaccording to claim 12, characterized in that the measuring units areconfigured as position measuring units.
 14. The method according toclaim 13, characterized in that the position measuring units areconfigured as rotary encoders.
 15. A system comprising a transmitter anda receiver, between which data are transmitted bi-directionally, whereinthe transmission of the data is carried out with the method according toclaim
 1. 16. The system according to claim 15, characterized in that thedata are exchanged between a controller of the transmitter and measuringunits of the receiver.
 17. The system according to claim 16,characterized in that the measuring units are configured as positionmeasuring units.
 18. The system according to claim 17, characterized inthat the position measuring units are configured as rotary encoders. 19.The method according to claim 3, characterized in that the some timedelay bits are 4 to
 7. 20. The method according to claim 5,characterized in that one or more stuff bits are inserted directlybefore the first bit length.